1. Field of the Invention
This invention relates to the field of magnetic recording media and more particularly to an improved method of manufacturing a flexible disk for digital data storage of a type having structural reinforcement in the region near the central aperture thereof.
2. Description of the Prior Art
A magnetic data storage medium comprising a circular flexible disk coated with magnetic material and enclosed in an envelope with apertures for accessing the disk has found wide use in the computer industry. Such assemblies have come to be called "floppy disk assemblies" or just "floppy disks". The flexible recording disks have a circular central aperture which is used to locate the disk with precise repeatable positioning on a spindle for rotating the disk, thereby allowing data transfer to and from the coating on the disk. Data is stored on the disk in narrow circular tracks concentric to the central aperture, so any eccentricity which results from the alignment of the disk on the spindle reduces the ability to recover recorded data. The region of the disk immediately surrounding the aperture is subject to stress and wear from both the insertion/mounting of the disk on the spindle, and the rotation of the disk. Normal usage thus results in wear and/or damage to the disk in the region of its central aperture. Ultimately this wear or damage results in inadequate alignment and unreliable data transfer during use.
Reinforcement of the region around the central aperture will extend the useful life of the disk, and various approaches have been offered for achieving such reinforcement. An aperture reinforcement achieved by adhesively bonding an annular-shaped piece of structural material to the flexible disk about its central aperture is described in U.S. Pat. No. 4,052,750 issued to Barber, et al. Fabrication of floppy disk assemblies in accordance with that disclosure requires precise alignment between the inner edges of the aperture of the disk and the annular-shaped reinforcing member. Floppy disks manufactured in accordance with the Barber, et al specification may exhibit the migration of the adhesive and result in contamination of the spindle with that adhesive.
Aperture reinforcement achieved by transferring a liquid polymer material to an annular-shaped region around the central aperture of the disk and curing the liquid to form an integral reinforcement is described in U.S. Pat. No. 4,387,114 issued to Conner, et al. While a disk manufactured in accordance with that patent avoids any possibility of adhesive migration, it still requires precise alignment of the reinforcing structure with the aperture of the disk in the manufacturing process. The process in that specification requires lifting a quantity of liquid from an annular-shaped reservoir and printing that liquid in a precise region around the central aperture of the disk, by a reciprocating motion of a flexible rubber tampon. The precise locating of the flexible rubber tampon alternately on the reservoir and the disk is both slow and expensive.
The thickness of the reinforcing structure on the disk affects the clamping pressure in common spindle designs. The thinner the reinforcement, the less the clamping force varies from the expected clamping force attained with disks without reinforcement. It is therefore preferable to minimize the thickness of the reinforcing structure, so long as sufficient structural reinforcement is attained. The Conner, et al specification refers to a maximum thickness between 0.0003 and 0.0005 inches for the reinforcement on the disk. This is thinner than that which can be attained with the structure disclosed by Barber, et al, which results in a total increase in the thickness of the disk of up to 0.016 inches if both sides of disk are reinforced. A thinner reinforcement allows more consistency with the dimensions of unreinforced disks for which the spindles were originally designed.